Most domestic dishwashers include two dish racks to support items to be washed such as dishware, glassware, kitchen utensils, pots, pans and the like.
Typically, the two dish racks include an upper rack positioned near a top portion of the dishwasher, and a lower dish rack arranged below the upper rack. The upper dish rack is used to support glassware, utensils and other small items, while the lower dish rack is used to support larger items, such as dinner plates and backing pans.
Dishwasher racks need protection from the constant spurts of hot water and harsh detergents that churn through every dishwashing cycle. Design of choice is thus customarily based on frames made of steel wire coated with a plastic material.
Dish support racks need exhibiting appropriate mechanical properties, so as to resist to wear and impact caused by the contact with dishware and not to be scraped off with a fingernail or an errant fork or knife. To this aim, thus, the selection of an appropriate coating plastic material has focused on polyamide materials. Generally color of the coating varies according to the design of the machine equipped with the rack and is achieved by adding commercial pigments to the coating. While the selection of the coating is not critical, it is nevertheless customary to employ at least one opacifying filler or pigment in the coating compound.
Thus, US 20010032825 (DEGUSSA-HUELS AG) 25, Oct. 2001 discloses a dish rack for a dishwasher, including a frame and a coating covering the frame and configured to distribute water over a surface of the coating in a thin film, wherein said coating may be plastic, substantially polyamide.
Similarly, DE 19917151 A (MIELE) 19, Oct. 2000 discloses a dish support rack for dishwasher formed from a wire basket coated with a polyamide material or with polyethylene. More specifically, this document discloses polyamide 11 and polyamide 12 as preferred materials over polyamide 6 and polyamide 6,6, and over polyethylene. Underlying rationale provided in this document is that performances of the plastic coating material are deeply influenced by the ratio between the number of methylene groups (—CH2—) and the number of amido-group (—CO—NH—), the higher this ratio, the better being the oil resistance and the lower the water absorption, and the more limited being hydrolytic depolymerisation phenomena. Within this scenario, thus, PA11 and PA12 were found to be best performers for optimal coating of metal wires of dish support racks.
Nevertheless, the relatively large number of methylene groups in PA11 and PA12 make the threshold for plastic deformation relatively low: in other terms, even relatively low stress applied might cause plastic deformations which cannot be recovered. As a whole, thus, dish racks coated with PA11 or PA12 might be relatively sensible to deformation and giving whitening phenomena and possibly failures.
A continuous need in the art thus exists for polyamide-based compositions suitable for coating dish support racks in dishwashers, delivering outstanding resistance to chemically harsh environments, and possessing improved mechanical properties.